1. Field of Invention
The present invention relates generally to the field of wireless communication and data networks. More particularly, in one exemplary aspect, the present invention is directed to wireless communications system using multiple air interfaces and multiple antennas.
2. Description of Related Technology
Wireless connectivity is becoming ubiquitously available and necessary in electronic computing, information, and entertainment products. Presently, many electronic products such as mobile phones, computers, media players, etc. come equipped with one or more wireless networking or communication interfaces.
In many cases, these communication interfaces may include both wired and wireless network interfaces. Wireless network interfaces, also called “air interfaces”, are of increasing interest due to the mobility and freedom they afford a user. Exemplary wireless networking technologies include Wi-Fi (IEEE Std. 802.11a/b/g/n), WiMAX (IEEE Std. 802.16e, etc.), PAN (IEEE Std. 802.15), IrDA, ultra-wideband (UWB), Mobile Wideband (MWBA; IEEE-Std. 802.20), Bluetooth (BT), and others.
Many popular electronic devices now also utilize multiple air interfaces in ways where interference between these air interfaces can cause problems with the function or “user experience” (i.e., user enjoyment or perception of functionality) of the device. One common implementation for portable electronic devices is the simultaneous use of Wi-Fi and BT air interfaces or radios, which operate in overlapping frequency bands. Accordingly, when a WLAN 802.11b/g/n and BT radio are integrated in a personal electronic device, and because these two radios share the same frequency band (i.e., the Industrial, Scientific and Medical (ISM) band of 2.4-2.48 GHz), there is interference between the radios when they operate simultaneously. However, BT was designed with the possibility of radio interference in mind, and utilizes algorithms that are adapted to mitigate the effects of EMI or external emissions, including a feature known as adaptive frequency hopping (AFH), described in greater detail subsequently herein.
Traditionally, as long as the WLAN and BT modules have over 40 dB isolation and the aforementioned BT AFH algorithm is implemented properly, in most cases the interference between WLAN and BT is not very noticeable, and the user experience for WLAN and BT simultaneous operation is reasonable, especially in cases where the isolation is sufficiently large (e.g., >35 db between the first and second air interface antennae).
However, with the evolution of new applications for these wireless systems, as well as shrinking system form factors, existing methodologies and algorithms are becoming increasingly insufficient. For example, most prior art WLAN usage cases were for downloading; e.g., receiving email, web surfing, and streaming audio/video applications. Accordingly, for the majority of the time, WLAN was used almost exclusively for receiving data, thereby resulting in a lower probability of interference between the WLAN module (i.e., during WLAN transmissions) and the BT module that is mostly used in a receiving mode. This results from the fact that most common implementations for BT in portable computing devices are for a BT human interface device (HID), such as a mouse (MS), touch pad, headset, and/or keyboard (KB).
More recently, manufacturers have fielded products which provide increasing amounts of usage for the transmit side of the portable device's WLAN module than had been previously experienced in prior implementations. For example, the Assignee hereof has developed products such as Apple TV™ and Apple Time Capsule™, which, in combination with a user's existing computing device(s), increase usage of WLAN transmit functions. As illustrated in FIG. 1, a user of a computing device 100 (such as for example the MacBook Pro™ device), might have his/her software storage application (e.g., Time Machine™) upload files to a remote Wi-Fi capable storage device 110 (e.g., such as their separate Time Capsule hardware), while simultaneously utilizing a BT MS/KB 120 as the default HID. In addition, when utilized with external displays, such as Apple's LED Cinema Display, the computing device 100 (if a laptop computer), is often operated in its clamshell mode (i.e., closed) which tends to negatively affect isolation between the two antennas.
As a result of this increased amount of usage on the transmit side of the WLAN interface (and/or decreasing levels of isolation in certain operational modes), the probability of interference from the WLAN 115 (e.g. during transmitting or sync-up of files sent to the storage device 110, etc., as shown in FIG. 1) affecting BT operation 125 (e.g. receiving from the MS/KB periodically, etc.) increases. In the aforementioned exemplary scenario, a WLAN and BT antenna isolation of 40 dB provided using only the default BT AFH is no longer sufficient to provide an acceptable user experience. In other words, users will start to notice a significant degradation in service quality, which can manifest itself for instance as jerkiness or other undesired motion or artifact when utilizing a BT MS.
The foregoing problems are yet further exacerbated by the push towards smaller form factors (thereby tending to reduce isolation), as well as packaging with less-than-ideal materials for wireless system implementation (such as the metallic housing or case structures), thereby complicating efforts to increase isolation between wireless network interfaces in the foregoing use cases.
Moreover, battery-powered BT peripheral devices are constrained on their power use. Poor isolation can lead to the increase of BT transmission power (e.g. from class 2 to class 1) and potentially an increased number of BT data retransmissions, both of which result in shorter battery life and decreased levels of user satisfaction.
Despite a variety of attempts to address interference associated with multiple air interface co-existence evidenced in the prior art (including the aforementioned BT AFH scheme, transmitter power control schemes based entirely on RSSI (Receiver Signal Strength Index), and so-called “time sharing” approaches described in greater detail below), there is a salient need for improved methods and apparatus that provide additional robustness against interference in systems that operate in historically untraditional ways. Specifically in the context of the aforementioned WLAN transmission usage case, there is a need for a solution which addresses poor user experience with one or more air interfaces. Ideally, such a solution will also address situations that are highly space-constrained or otherwise necessarily result in low isolation values between the antennae of the various air interfaces of the platform (for example, WiFi/WLAN and Bluetooth, WiMAX and Bluetooth, WLAN and UWB).
Such an improved solution would ideally permit for good user experience by avoiding significant audio or data drop-outs; prevent the appearance of adverse effects on data streaming rate; avoid the preclusion of use of one interface when another is being used; and be absent of any significant operation restrictions with respect to the multiple air interfaces by allowing two or more interfaces to operate simultaneously in at least a partial capacity. Furthermore, such a solution would still obey the platform or form-factor limitations such as those present in extremely small hand-held or laptop computing devices, or those with metallic cases which inherently present challenges to antenna placement.